1. Field of the Invention
This invention relates to coating materials and processes and more particularly to the protection of roof surfaces with coatings which are highly adherent to these surfaces, and resistant to water ponding and long-term weathering. The coatings additionally may be formulated to have excellent flame retardancy.
2. Description of the Prior Art
The use of built-up asphalt, known as "BUR" in the building industry, has been the standard system for covering flat and gently pitched roofs in the United States for well over a century. The asphalts used in this system are dispersions of asphaltenes (heavy molecular weight) and maltenes (resins and oils). Weather oxidizes and hardens asphalts, destabilizing the oils in the maltene fraction and causing them to "sweat" to the surface. Loss of oils reduces the flexibility of the roof membrane and causes the BUR surface to crack under the sun.
Roof coatings seal the BUR membrane, preventing loss of oils and preserving the needed flexibility. White roof coatings additionally provide high reflectance which reduces thermal shock movement and membrane fatigue. The presence of protective roof coatings also eliminates or greatly reduces the need for dead load gravel which can eventually cause roof assembly deflection.
Coatings of the present state of the art have not been entirely successful. A particular problem results from loss of adhesion to roof substrates, particularly hot-mopped asphalt, after areas of the roof have been under water for prolonged periods of time. Without adhesion to the wet areas, the protective film eventually blisters away from the substrate, leaving the surface without protection.